Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
editing
approved
a(0)=2, since 2 is the least number with zero non-prime nonprime substrings.
a(1)=1, since 1 has 1 non-prime nonprime substrings.
a(2)=10, since 10 is the least number with 2 non-prime nonprime substrings, these are 1 and 10 (‘'0’ ' will not be counted).
a(3)=14, since 14 is the least number with 3 non-prime nonprime substrings, these are 1 and 4 and 14. 10, 11 and 12 only have 2 such substrings.
approved
editing
reviewed
approved
proposed
reviewed
editing
proposed
With b(n):=floor((sqrsqrt(8*n-7)-1)/2):
approved
editing
editing
approved
Minimal Smallest number with n non-prime nonprime substrings (Version 3: substrings with leading zeros are counted as non-prime nonprime if the corresponding number is not a prime).
The sequence is well defined since for each n >= 0 there is a number with n non-prime nonprime substrings.
Different from A213303, first different term difference is at a(16).
nonn,changed,base
proposed
editing
editing
proposed